Add SD card disk boot support for NXP T1040 (eSDHC)

[dgarske]

This PR adds SD card disk boot to the NXP QorIQ T1040 (PPC e5500) using the on-chip Freescale eSDHC controller, making it the first big-endian target to use the src/update_disk.c boot path: wolfBoot reads the signed image from GPT/MBR A/B partitions on the card, picks the higher version, verifies it and boots it from RAM.

[Copilot]

Pull request overview

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Adds SD-card disk boot support for NXP QorIQ T1040 (big-endian PPC) via the on-chip eSDHC controller, and updates GPT/MBR parsing to be endian-correct across hosts/targets.

Changes:

• Implement new eSDHC-based disk_* backend for PPC and wire disk boot (update_disk) into the nxp_t10xx build.
• Refactor GPT/MBR parsing to read on-disk fields byte-wise (LE) instead of via packed structs; expand unit tests accordingly.
• Update linker scripts and documentation/config to support SD disk boot on T1040.

Reviewed changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
tools/unit-tests/unit-disk.c	Makes the GPT/MBR fixtures endian-robust and adds offset/CRC regression tests.
src/gpt.c	Switches GPT/MBR parsing to explicit little-endian loads and avoids packed-struct aliasing.
src/disk.c	Makes MBR partition parsing endian-correct by reading fields via LE helpers.
include/gpt.h	Adds shared gpt_le16/32/64 helpers and MBR field offsets.
hal/nxp_esdhc.c	Adds a new eSDHC SD-card PIO block driver implementing disk_* API for PPC.
hal/nxp_t10xx.c	Includes the eSDHC driver into the HAL translation unit for access to static clock helpers.
arch.mk	Selects disk-boot update path and links src/disk.o for nxp_t10xx when SD/eMMC is enabled.
options.mk	Avoids linking Cadence SDHCI driver on PPC to prevent symbol collisions with eSDHC backend.
hal/nxp_t1040.ld / hal/nxp_t1040_stage1.ld	Adjusts DRAM LENGTH constants around the 2GB boundary.
hal/nxp_t1024.ld / hal/nxp_t1024_stage1.ld	Same DRAM LENGTH adjustment for T1024.
config/examples/nxp-t1040-sdcard.config	Adds a sample config enabling SD disk boot and related limits/defines.
docs/Targets.md	Documents T1040 SD-card boot workflow and example partitioning.

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